Bi-Doped P2 layered Sodium-Ion Battery Cathode with Improved Cycling Stability

Abstract

P2-phased layered oxide materials have been extensively studied as cathode material for sodium-ion batteries due to their high capacities and ionic conductivities, making them promising for large-scale applications. Additionally, manganese-based compounds, with their low cost and high capacity, have attracted significant attention in recent years. However, challenges remain regarding durability issues and related structural instability caused by the Jahn-Teller effect induced by Mn3+ ions formed during the cycling process in these materials, which causes manganese dissolution during use. In this study, we introduce a cathode composition of Na0.8Mn0.75Fe0.2Al0.05O2 and show that bismuth doping enhances the structural stability of the cathode material during electrochemical cycling. Electrodes with varying levels of bismuth doping were compared in half-cell configurations; material with 1% bismuth doping demonstrated outstanding stability, retaining 95.8% capacity after 200 cycles at a 0.2 C rate through the full potential range. dQ/dV analysis shows that bismuth doping effectively suppresses the excess Mn redox, which could otherwise deteriorate the cathode structure. As a proof of concept, Bi-doped materials were implemented in full cells paired with hard carbon that exhibited much better stability than those without bismuth doping. Lastly, the moisture and air stability of the bismuth-doped electrode were tested, demonstrating good stability.